- Title
- The ryanodine receptor pore blocker neomycin also inhibits channel activity via a previously undescribed high-affinity Ca²⁺ binding site
- Creator
- Laver, Derek R.; Hamada, Tomoyo; Fessenden, James D.; Ikemoto, Noriaki
- Relation
- Journal of Membrane Biology Vol. 220, Issue 1-3, p. 11-20
- Publisher Link
- http://dx.doi.org/10.1007/s00232-007-9067-3
- Publisher
- Springer
- Resource Type
- journal article
- Date
- 2007
- Description
- In this study, we present evidence for the mechanism of neomycin inhibition of skeletal ryanodine receptors (RyRs). In single-channel recordings, neomycin produced monophasic inhibition of RyR open probability and biphasic inhibition of [3H]ryanodine binding. The half maximal inhibitory concentration (IC₅0) for channel blockade by neomycin was dependent on membrane potential and cytoplasmic [Ca²⁺], suggesting that neomycin acts both as a pore plug and as a competitive antagonist at a cytoplasmic Ca²⁺ binding site that causes allosteric inhibition. This novel Ca²⁺/neomycin binding site had a neomycin affinity of 100 nM and a Ca²⁺ affinity of 35 nM, which is 30-fold higher than that of the well-described cytoplasmic Ca²⁺ activation site. Therefore, a new high affinity class of Ca²⁺ binding site(s) on the RyR exists that mediates neomycin inhibition. Neomycin plugging of the channel pore induced brief (1-2 ms) conductance substates at 30% of the fully open conductance, whereas allosteric inhibition caused complete channel closure with durations that depended on the neomycin concentration. We quantitatively account for these results using a dual inhibition model for neomycin that incorporates voltage-dependent pore plugging and Ca²⁺-dependent allosteric inhibition.
- Subject
- ryanodine receptor; neomycin-ryanodine binding; bilayer; single channel recording
- Identifier
- http://hdl.handle.net/1959.13/44499
- Identifier
- uon:5776
- Identifier
- ISSN:0022-2631
- Language
- eng
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